Radioembolization using Y-90 microspheres delivered into the hepatic artery under fluoroscopy guidance has slowed tumor progression in the liver for patients diagnosed with metastatic colorectal cancer (mCRC). Treatment planning is based on a simple estimate of the average absorbed dose (AD) delivered to the treated volume; tumor dose thus depends on tumor burden and tumor-to-background ratio, resulting in under-dosing in some patients. Dosing based on more rigorous, patient-specific AD to normal liver would allow safely increasing administered activity, likely improving tumor response, without an increased toxicity. The goal of this work is to improve the outcome of patients with mCRC by implementing a cloud-based treatment planning software service using rigorous quantitative imaging and dosimetry methods. We will perform a pilot study involving 3 patients to demonstrate feasibility of recruiting, imaging, and performing the treatment planning, validate the reproducibility catheter placement, add and verify quantitative Tc-99m MAA SPECT/CT reconstruction capability, verify that AD to normal treated liver estimated from Tc-99m MAA predicts the normal liver AD measured using quantitative Y-90 bremsstrahlung SPECT, validate automated segmentation of liver in Tc-99m MAA SPECT/CT images, develop and validate a proof-of-principle cloud-based software service; and obtain approval for the Phase II project?s dose escalation trial.